High temperature diffusion tube

ABSTRACT

A quartz tube designed for use at temperature in excess of 1,200* C. is provided with a plurality of external reinforcing ribs integral with the tubular body member.

w 0 A .s ,g United States Patent 1191 1111 3,7964 Hart [4 .Huiy 10, 11973 1 HIGH TEMPERATURE DIFFUSION TUBE 3,519,255 7/1970 P 263/41 X 3,020,032 2/1962 C 263/42 R Inventor: Melvln Gary Hart, Richardson, Tex. I l l u R [73] Assigneez Texas Instruments Incorporated, 1,549,191 8/1925 Fisher .1 263/42 R Dallas Tex 2,381,538 8/1945 Hams 263/47 R [22] Filed: May 1971 Primary ExaminerJohn .1. Camby {21] App]. No.: 147,948 Attorneyjames 0. Dixon, Andrew M. Hassell, Harold Levine, Melvin Sharp, Michael A. Siieo, Jr., Gary C. {52] 1.1.8. Cl. 432/120 333253 3 dlgnff Stephen Sadacca and [51] Int. Cl. F27b 5/00 [58] Field of Search 263/41, 42, 47 R;

432/120 [57] ABSTRACT A quartz tube designed for use at temperature in excess [56] References Cited i of 1,200 C. 15 provided with a plurahty of external re- UNITED STATES PATENTS inforcing ribs integral with the tubular body member. 170,430 11/1875 Armstrong 263/41 X 2,671,123 3/1954 Sherrick 4 Claims, 1 Drawing Figure Patented July 10, 1973 3,744,964

I/VVEA/TQ/P Me/w'n 6214/0 ATTORNEY HIGH TEMPERATURE DIFFUSION TUBE This invention relates to high temperature quartz tubing designed to have an extended lifetime at working temperatures in excess of l,200 C., and to methods for the fabrication of such tubing. In a specific embodiment, the invention relates to a furnace structure including such a tubular quartz member.

In the fabrication of semiconductor devices, it is a common practice to subject semiconductor wafers to temperatures in excess of l,200 C. for extended periods of time for various purposes, including the diffusion of impurities. A diffusion furnace employed in such processing is usually provided with a removable tubular quartz lining. At the temperatures employed, the quartz tube has been found to experience a relatively short lifetime, with failure usually occuring by means of gradual distortion and sagging of the tube wall, forcing frequent replacement.

The use of heavy wall" tubing has been proposed as a solution to the problem. However, the added expense of heavy wall tubing is quite significant since the additional lifetime achieved is relatively short. Accordingly, it is an object of the present invention to provide a mechanically reinforced quartz tube having a greatly extended lifetime at temperatures in excess of 1,200 C., and to provide a simple technique for the fabrication of such a tube.

It is a further object of the invention to provide an improved furnace combination having a tubular quartz lining characterized by an extended lifetime at temperatures in excess of l,200 C.

One aspect of the invention is embodied in a quartz structure comprising a tubular quartz body member having a plurality of external reinforcing ribs integral therewith. The reinforcing ribs are provided by a method which begins with the step of mounting a tubular quartz member on a rotary lathe of a type commonly employed in glass working operations. The tubular member is then rotated while heating a narrow annular section thereof with a hydrogen torch or other suitable heating means. When the temperature of the heated section reaches the softening point, a compressive axial force is applied in order to form an enlarged, external annular rib or ridge surrounding the tubular member. Thereafter a second narrow annular section, spaced apart from the first annular section, is heated to the softening point and the procedure repeated to form a second external annular ridge surrounding the tubular member. Additional such ridges are provided spaced at intervals of approximately 2 to 6 inches depending on the tube diameter, the overall length of the tube, and the intended operating temperature of the furnace wherein the tube is to be employed.

A further aspect of the invention is embodied in a furnace structure comprising in combination a tubular quartz member having a plurality of annular external ridges integral therewith, and a means for maintaining a substantial portion of said tubular quartz member at a temperature in excess of l,200 C.

The drawing is a cross-sectional view of a diffusion furnace, including a tubular quartz member lll fabricated in accordance with the invention. Member 11 includes annular external ridges l2 integral with tubular body member. it is particularly significant that the internal surface of the tube wall is substantially uniform; that is, the ridges 12 are substantially entirely external, thereby presenting a minimum interference to the loading and unloading of furnace boats containing semiconductor wafers or other materials to be processed. Heating means 13 which surround the tube includes electrical resistance heaters or other suitable means for maintaining tube 11 at temperatures at excess of l,200 C.

For example, the illustrated tube has an overall length of about inches. The inside diameter is 70 millimeters and the outside diameter 74 millimeters. The outside diameter of ridges 12 is about 87 millimeters. The spacing between ridges is about 4 inches. in actual test runs the tube of the invention has been shown to have a lifetime at least five times greater than the lifetime of a conventional quartz tube subjected to the same temperatures.

It will be apparent that the invention is also applicable to glass tubing of all kinds; not quartz alone. However, in the case of ordinary glass, it is normally more convenient to substitute a stronger glass instead. Since quartz tubing is the strongest of the commonly available glasses, the practical value of the invention may be limited to quartz.

In the illustrated example, tube 11 is supported by ridges 12 in contact with the wall of furnace 13. it will sometimes be desirable, however, to support the tube at each end only, in which case the reinforcement technique of the invention also provides a dramatic increase in lifetime.

What is claimed is:

1. A furnace structure comprising in combination a tubular quartz member having a plurality of annular external ridges integral therewith, and means for maintaining said member at temperatures in excess of l,200 C.

2. A furnace structure as in claim 1 wherein said annular external ridges are spaced at intervals of 2 to 6 inches along the length of the tubular quartz member.

3. A furnace structure as in claim 2 wherein the walls of said tubular quartz member have a thickness of about four millimeters.

4. A furnace structure as in claim 3 wherein said tubular quartz member is supported within said furnace structure by means of direct contact of the annular external ridges with the walls of the furnace structure. 

1. A furnace structure comprising in combination a tubular quartz member having a plurality of annular external ridges integral therewith, and means for maintaining said member at temperatures in excess of 1,200* C.
 2. A furnace structure as in claim 1 wherein said annular external ridges are spaced at intervals of 2 to 6 inches along the length of the tubular quartz member.
 3. A furnace structure as in claim 2 wherein the walls of said tubular quartz member have a thickness of about four millimeters.
 4. A furnace structure as in claim 3 wherein said tubular quartz member is supported within said furnace structure by means of direct contact of the annular external ridges with the walls of the furnace structure. 